The use of hydraulic power to operate cranes has been known and examples appear in the patent literature from an early time. Some of the more recent and more sophisticated examples can be found in U.S. Pat. Nos. 2,906,143, 2,984,191, 3,872,671, 3,872,674 and 3,907,120. Examples are also found in British patent literature and reference is made to British Pat. No. 954,652 and No. 954,653.
Despite recognizing the possibility of adopting hydraulic prime movers the hydraulic crane has not met with any significant commercial success. There are many reasons which contribute to this but principal among the stated or acknowledged disadvantages is the tendency for hydraulic motors to leak or discharge oil. This is viewed as very undesirable in most situations where cranes will operate.
I believe the advantages which can be secured from the successful operation of a hydraulic crane considerably outweighs the disadvantages particularly in view of the very high component cost necessary in an electrically powered crane and the high maintenance costs required to ensure satisfactory long term operation of such a crane. By way of an example of such a disadvantage reference is specifically made to the energy dissipation means which must be incorporated in an electrically powered crane and these overheat and can lead to high maintenance costs or failure. I believe all these disadvantages can be overcome by the adoption of a hydraulically operated crane.